1. Field of the Invention
The present invention relates generally to a carbonless copying system wherein mating sheet surfaces are coated respectively with compatible initially colorless reactive components capable of reacting to produce a colored mark upon impact. More particularly, the invention relates to manifold sets utilizing both single and dual initially colorless color forming systems whereby it is possible to produce a colored mark on both sides of such sheets by impact.
2. Description of the Prior Art
Manifolded sets of carbonless copying paper normally comprise a top sheet, a bottom sheet and at least one intermediate sheet disposed therebetween. The top sheet which is conventionally coated on its back surface with an encapsulated solution of a colorless color-former in a suitable solvent and is generally therefore referred to as CB ("Coated Back") paper. The bottom sheet conventionally has its front surface coated with a solid material containing a record-developing material and this "front coated" sheet is generally referred to as CF paper. The intermediate sheets are often coated respectively with the above-mentioned solid record-developing material in the front coatings and with the color precursor in the back coatings and accordingly such "front and back coated" sheets are referred to as CFB paper. The back coatings normally comprise pressure rupturable microcapsules containing a fluid color precursor in fluid form which is capable of reacting to thereby form a colored compound with the developing material in the front coating of the next adjacent sheet so that, upon impact by a machine key or application of pressure by a stylus on the top sheet, the contents of the ruptured capsules in the back coatings spill out and react with the developing material to form a colored mark on the latter which corresponds to the mark impressed by the stylus or machine key.
The present invention relates generally to a co-pendng and commonly owned U.S. application Ser. No. 466,910, filed May 3, 1974, and entitled "DUAL SYSTEM CARBONLESS PAPER", now abandoned the entirety of the disclosure of which is hereby specifically incorporated herein by reference. In this regard it is to be noted that the present application also relates to dual systems of co-reactive materials; however, the present invention differs from that of the above-mentioned application in its construction and purpose as will be more clearly brought out hereinafter.
Although, in conventional manifolded carbonless copying sets, the back coatings normally comprise a microencapsulated solution of the color precursor and the front coatings normally comprise a solid record-developing material, it should be pointed out that the reverse is also possible so that the front coatings comprise microcapsules and the back coatings comprise a solid record-developing material. Moreover, the co-reactants may both be microencapsulated liquids. United States patents which illustrate various types of systems which may be used in the production of carbonless transfer papers are, for example, U.S. Pat. No. 2,299,694 to Green, U.S. Pat. No. 2,712,507 to Green, U.S. Pat. No. 3,016,308 to Macaulay, U.S. Pat. No. 3,429,827 to Ruus and U.S. Pat. No. 3,720,534 to Macaulay et al.
The aforementioned Green (U.S. Pat. No. 2,712,507) and Macaulay (U.S. Pat. No. 3,016,308) patents illustrate the most common variety of carbonless impact transfer paper of the type with which the present invention is primarily concerned wherein microcapsules containing a liquid fill comprising a chemically reactive color-forming precursor are coated on the back surface of a sheet, and a dry coating of a solid co-reactant chemical for the precursor is coated on the front surface of a receiving sheet.
In the current carbonless copying systems of the type aforedescribed the image is usually developed on the front sides of the sheets. In certain cases, however, it is desirable and advantageous for images to be produced on both sides of several or all sheets of a set of manifold business forms. Depending on the particular business needs, various types of entries are required to be made on the sheets of a manifolded set of forms thereby requiring larger and more detailed sets of forms to be made which results in the need for more paper and precise printing techniques. Carbon transfer sheets have sometimes therefore been interleaved with carbonless paper systems so that, after an image is produced on the front side of the receiving sheet using the carbonless system, an image can also be produced on the back side of such receiving sheet by means of the conventional carbon transfer. The problems of carbon smudging, poor manifolding and difficulty in manufacture nevertheless persist in such an arrangement.
An interesting prior art reference is Japanese patent publication No. 43-28652. This patent discloses a carbonless duplicating notebook consisting of a set of initially colorless copying sheets containing pressure rupturable components for transfer of the color forming ingredients. The patent is basically directed to a base sheet having a first color forming reactant on each side thereof. A plurality of secondary sheets are provided each of which has one side thereof coated with a second color forming reactant reactable with the first color forming reactant to form a color and the second side thereof coated with the first color forming reactant. Sets are formed by placing the secondary sheets on either side of the base film with the second color forming reactant coated surfaces facing the first color forming reactant surfaces. However, this patent does not generally disclose the concept of having an image produced on each side of the sheets of the set.